The task to create networks covering large areas and spanning over vast distances, in environments where many wireless networks are simultaneously operating, have always been a challenge. Such environments are typically found in urban and industrial areas. In addition to the challenge to cover large areas, interference from other wireless devices will vary from one location to another. For instance, WiFi may be extensively used at one location in the network and thereby occupying a large portion of the available frequencies, and different frequencies may be occupied elsewhere in the network.
Furthermore, interference will vary over time due to the fact that some wireless networks are used more at certain hours of the day, and others new wireless networks may also be installed. An example of this is WiFi usage in a residential area which is often used more heavily during the evenings and weekends.
Traditional prior art techniques are well suited for small area networks such as a WiFi hotspot; a Bluetooth voice transfer from a headset to a mobile phone; and a wireless metering network. The prior art technique for interference free coverage in large area networks is to only allow signals within a frequency range for a specific wireless network, which often requires a governmental license. Examples of such networks are GSM and television broadcasting, see for instance EN 301 511, Global System for Mobile communications (GSM).
If a network is expanded to cover a large area where a number of WiFi networks and other wireless networks are operating, the problem with interference arises. The use of the same communication parameters, such as frequency, in the different networks may result in disrupted communication. Although the WiFi hotspots are out of range of each other, they are within the coverage area of the expanded large area network. It should be noted that not only the expanded large area network may be disrupted due to the interference between the networks, but most certainly the local WiFi networks will be disrupted resulting in a lower quality of service for the WiFi hotspots.
A typical example is a multi-storey office building having a WiFi network on each and every floor. Sometimes many local WiFi areas may be found on the same floor. The sum of all frequencies used within the entire building, which may be considered to be a large area network, results in a loss of available frequencies to use. This may result in communication drop outs. In addition to this, other wireless more mobile devices, such as wireless head sets, may be frequently used within the multi-storey building further increasing the density temporarily.
Reference [1] discloses a network divided into a number of clusters (subnets) that communicates internally using a local set of communication parameters. The cluster heads also may exchange communication between the clusters using a set of communication parameters. The communication is performed over a number of frequency channels divided into time slots. The intra-communication (within the clusters) and the inter-communication (between clusters) is performed sequential using the same frequency channels in different time slots.
Reference [2] discloses a network configured to adapt to a wireless environment, by allocating available resources.